Heretofore, a vehicle that mounts thereon a power train, which uses two kinds of power sources including a gasoline or diesel engine that is an internal combustion and an electric motor (motor generator) in combination, is put to practical use. Such a power train is called as a hybrid system.
A vehicle (hybrid vehicle) on which such a hybrid system is mounted can drive not only with collaboration driving between an engine and an electric motor but also with only the electric motor depending upon performance of an electric motor and a battery. In such a hybrid vehicle, in the case where driving force (torque) required from an electronic control unit exceeds torque that the electric motor can utilize during EV driving in which the vehicle is driven with only the electric motor, the stopping engine is to be restarted.
In order to restart the engine while stopping, it is need to supply engine starting torque depending upon temperature of the engine to the engine. For that reason, the electronic control unit has controlled the electric motor to drive with torque obtained by subtracting this engine starting torque from maximal torque of the electric motor during the EV driving.
Further, a vehicle provided with two motors (electric motor and electric generator) with respect to one engine is also put to practical use. In such a vehicle, it is proposed to correct engine starting torque with temperature (see Japanese Patent Application Publication No. 2005-163551 (hereinafter, referred to as “Patent Literature 1”), for example). In the power output apparatus disclosed in Patent Literature 1, an engine startability state such as temperature of the engine is detected, and it is controlled to start the engine until power required on the basis of this startability state reaches output restriction of the electric motor.
Moreover, in the vehicle provided with one engine and one motor generator, a control apparatus for a hybrid vehicle that a gear ratio is changed until torque required to start an engine is ensured and the engine is thereby started in the case where a request output (calculated by vehicle speed and an accelerator pedal position) from a user exceeds a solo driving possible region of the motor generator during EV solo driving by the motor generator has bee known (see Japanese Patent Application Publication No. 2000-177412 (hereinafter, referred to as “Patent Literature 2”), for example).